The present invention relates to a heat fluxmeter for checking calorigenic materials within a container.
It has numerous applications in widely differing nuclear and non-nuclear fields and particularly in the management of storage areas for calorigenic nuclear materials, where it makes it possible to measure the quantities of such materials in a very short time.
It is known that any radioactive element emits radiation which, if it is absorbed by the air or the material placed within the volume defined by the sensor, i.e. the cell of the calorimeter it is converted into heat. By measuring this heat quantity, it is possible to know for a given radioactive element the quantity of the radioactive product within the measuring cell. For example, it is possible to know the quantity of tritium in a tritiated compound, as a result of the emission of the .beta.-radiation of the tritium. In the same way, the radionuclides present in plutonium, americium, neptunium, etc. emit .alpha. radiation, whose energy is converted into heat in the very mass of the sample. This heat quantity is measured in a previously calibrated calorimeter. It is linked with the mass of plutonium, americium, neptunium etc. contained in the sample.
Such a calorimeter is described in French Pat. No. EN7203249. This apparatus uses as the detector a double electrical resistor, whose sensitivity is not very great. Therefore, the accuracy of the measurements is only acceptable when the temperature gradient between the two measuring resistors is adequate, which is obtained by separating the said resistors by a thermally insulating material.
Under these conditions, thermal equilibrium is only reached after about 10 or 20 hours and during this time it is necessary to maintain the reference temperature as constant as possible and checks must be made at regular intervals.
Finally, the known fluxmeter is a costly instrument, is not easy to use, is difficult to transport and is also not suitable for all container types.